What makes us tired when we ride? Pretty much everything, it seems, from the climbs to the descents, the terrain, the temperature and even how well we slept last night. Dr Shaun Phillips writes.

Dr Shaun Phillips

Dr Shaun Phillips

The good news is we can normally keep riding if we ease back a little (as opposed to exhaustion, where we simply cannot keep riding at all). However, fatigue will still limit our performance, so it’s useful to try to understand it a little more in order to minimise its impact.

Even the best mountain bike athletes in the world will suffer from fatigue frequently, so you’re not alone out there.


Your expert: Dr Shaun Phillips

Shaun is an old hand at understanding fatigue – a senior lecturer in Sport and Exercise Physiology at The University of Edinburgh, with over 12 years of experience teaching and researching. He’s new to mountain biking though, and thoroughly smitten.

What is fatigue?

No matter the trail, weather, your skill level or fitness, there is one thing all mountain bikers have in common; at some point, we will reach the limit of what our body is capable of. The tell-tale signs may be different; from bursting lungs to burning muscles to our mind begging us to ease back; but the outcome is the same – we are going to have to drop the intensity of our ride if we want to continue. We are experiencing fatigue.

This may seem incredible, but researchers have not agreed on a universal definition of fatigue in sport and exercise. The lack of a universal definition is important for one good reason: how can you fully understand something if you can’t even define it? The scientific literature is filled with dozens of definitions of fatigue, which are likely driven in part by the expertise of the scientists doing the research (e.g. a muscle physiologist will likely define fatigue with the muscle as the focus, whereas a cardiovascular researcher may focus on that system as the source of fatigue).

Tiredness can rapidly ramp up in hilly terrain

Tiredness can rapidly ramp up in hilly terrain

What causes it?

There are a multitude of influencing factors. In fact, the range of factors that can influence how an individual experiences fatigue during training or competition is almost unlimited. Broadly speaking, though, they can be broken down by the individual, the environment and the activity – see table below.

Causes of fatigue

Causes of fatigue

To further complicate matters,any and all of the factors in the table above can influence one another, meaning that you must look at the overall picture in order to understand fatigue in any given context. Mountain biking is a prime example of this, as there is one person on the bike (so all of the INDIVIDUAL factors are relevant), it is a sport hugely affected by the ENVIRONMENT, and it is a physically demanding activity requiring a host of different physical attributes from the whole body (ACTIVITY). We could even add a fourth category of EQUIPMENT to cover all of the influencing factors associated with the bike and rider gear, but we won’t go there!

Heads, shoulders, knees, toes (and everywhere else…)

The third challenge is that fatigue can occur in pretty much any body system, organ or process, and the fatigue
you experience will almost always be affecting more than one system/organ/ process. Of course, riding a mountain bike relies on appropriate contractions of the leg muscles. For those contractions to occur, electrical signals must originate in your brain, travel down your spinal cord, through peripheral nerves in your lower limbs, and into your leg muscles. This stimulates complex chemical processes within your muscles that enable them to contract. So, any disruption in any of these processes can cause fatigue.

But it’s more than just that. What if it’s a hot, humid day, and you are losing a lot of fluid trying to regulate your body temperature? Or how about a strong, persistent headwind, causing you to expend more energy than you anticipated? Perhaps your riding partner switched the route on you at the last minute, so you’re now doing much more aggressive climbing and descending than you’d anticipated. Now, as well as those electrical signals, you’ve got your cardiovascular system (temperature regulation), energy availability (headwind), and anaerobic/aerobic systems (climbing/descending) involved too. Hopefully you can see how easily the number of body systems, organs and processes potentially involved in fatigue, can exponentially increase.

Take-home messages

Learning a little about fatigue in sport and exercise can give us a real appreciation for and celebration of the amazing machines that are our bodies, and the truly whole-body demands and benefits that mountain biking can afford us. In the next issue we’ll look at what we can do to adapt our riding to stave off fatigue, but in the meantime remember:

Fatigue is a complicated thing

It’s complicated in part because we can’t fully define it, there are many factors that influence how it manifests, and it can affect almost any region of the body.

To hone in on how fatigue may be affecting you, think INDIVIDUAL, ENVIRONMENT, and ACTIVITY (and EQUIPMENT, if you’re feeling brave!).